appropriate since there would be too much heterogeneity within cells. These two requirements for few cells and homogeneous cells run against each other. The panel presents an attempt at the creation of a practical taxonomy, but this is only a preliminary attempt at such a construct. It is important to keep in mind that the kinds of military systems under development is an extremely dynamic process. The systems that are under development today are tremendously different from those developed in the 1950s. Therefore, any taxonomy would have to be reevaluated on a regular basis, and flexibility of the implementation of such a taxonomy would be very important. Further, there is no reason why a taxonomy is the preferable construct. Another possibility is a type of checklist, where answers to a succession of questions about system characteristics add different types of features to the recommended operational test.

Following is a discussion of characteristics that may affect the nature of the operational test of a military system. Boxes C-1 and C-2 list some of the many characteristics considered for inclusion in our taxonomy. These potential taxonomy dimensions have been divided into two broad categories, (1) those which have a broader application but probably do not have a direct bearing on the operational test, and (2) those dimensions which may have a direct bearing on how an operational test is designed and how preparations are made for it.

The panel selected three characteristics that seem important for test design. The taxonomy is designed to serve the following purposes:

Reflect the prevalence of various types of systems;

Highlight attributes that might call for different statistical approaches, affect decision trade-offs, or involve qualitatively different consequences; and

Provide a framework for developing the test scenarios.

A USEFUL TAXONOMY

The panel has developed a taxonomy for defense systems for the purpose of classifying systems by their operational test design needs rather than the uses to which the system will be put. For example, if the test issues and the type of data collected to address those issues are similar for a missile and a combat aircraft, then the taxonomy should put these two systems together in the same category. On the other hand, if say, a telephone for administrative use and a similar telephone for transmissions of intelligence information have quite different test issues, then the taxonomy should put them in different categories.

The panel's taxonomy has a broader conceptual base and utility than test design, however. A proper taxonomy entails notions of the loss function underlying the decision of whether to enter into full-rate production—since that is the purpose of operational test—and as discussed above, this decision directly involves the issue of test benefit versus test cost. To understand the benefit gained from the use of various test scenarios, one must consider the likely variability of

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